In order to increase the effective thrust of turbojet engines, bladed fans have been added to a turbine driven shaft thereof to effect the flow of a quantity of atmospheric air through an annular bypass duct surrounding the turbojet. Hot gases from the core engine and the bypass air stream are mixed together before expulsion through a single nozzle. In order to perform the mixing function, turbine exhaust case (TEC) mixers have been devised which include circumferential inner and outer flow surfaces extending between upstream and downstream ends of the mixer. The inner and outer flow surfaces have a twist extending toward the downstream end to form a plurality of lobes of the mixer, each of the lobes defining an internal passageway along the inner flow surface for the exhaust gases flowing through the mixer and each pair of adjacent lobes defining therebetween an external passageway along the outer flow surface for the bypass air stream. In order to maintain the strength of the mixer while minimizing its weight, it has become common practice to form the mixer from a single sheet of structural material. However, stiffener rings may be required on the mixer in order to restrain its end motion when the mixer is directly welded on the outer duct of a TEC, particularly in large sized turbine machinery engines, in an effort to avoid durability issues due to mixer vibratory responses.
Accordingly, there is a need to provide an improved TEC mixer.